text: Isocyanides form coordination complexes with most transition metals. They behave as electron-rich analogues of carbon monoxide. For example tert-butyl isocyanide forms , which is analogous to . Although structurally similar, the analogous carbonyls differ in several ways, mainly because t-BuNC is a better donor ligand than CO. Thus,  is easily protonated, whereas its counterpart  is not.